A copper film has been grown in a damascene pattern by electrodeposition in order to form a copper interconnect of an integrated circuit. A continuous copper seed layer having excellent step coverage is essential for high-quality electrodeposition since it provides a conductive substrate and has an important role in improving copper nucleation. Conventionally, a copper seed layer has been formed by using an ionized physical vapor deposition (i-PVD) method. However, as a minimum feature size decreases, the i-PVD method will confront the scaling problem.
According to the i-PVD method, a bottom corner of a pattern in a micro device is formed in a very small thickness and an overhang is formed at a trench/hole inlet portion, which results in poor step coverage. In this case, if a copper seed layer formed by the i-PVD method is not properly deposited or an overhang is formed to block the inlet portion, an empty space is formed therein. Such a problem is worsened in a dual damascene structure. According to the International Technology Roadmap for Semiconductors (ITRS), it is expected to be difficult to fill a dual damascene pattern having an aspect ratio of 2.0/1.8 for wire/via in 2017. This results from that it is difficult to form a continuous copper seed layer by a PVD method due to the limitation in step coverage. Meanwhile, U.S. Pat. No. 6,492,268 discloses “Method of forming a copper wiring in a semiconductor device”, but uses a physical vapor deposition so as to still have the above-described problem.
Atomic layer deposition (ALD) of a copper film has been researched using organic copper compounds such as copper(II)-2,2,6,6-tetramethyl-3,5-heptandionate [Cu(thd)2], copper(II) acetylacetonate [Cu(acac)2], copper(II)-1,1,1,5,5,5-hexafluoroacetonate [Cu(hfac)2] and its hydrate [Cu(hfac)2.xH2O], copper(I) N,N′-di-sec-butyl-acetamidinate [(Cu(sBu-Me-amd))2], bis(dimethylamino-2-propoxy)copper(II) [Cu(dmap)2], bis(1-dimethylamino-2-methyl-2-butoxy)copper(II) [Cu(dmamb)2], bis(1-(dimethylamino)propan-2-yloxy)copper(II), copper(II)(4-ethylamino-pent-3-ene-2-onate)2, and Cu(ethylketoiminate)2. As a reducing agent, hydrogen, hydrogen plasma, an alcohol or formalin, diethyl zinc (Et2Zn), and formic acid/hydrazine have been used. Copper(II) (1,1,1,5,5,5-hexafluoroacetylacetonate)(trimethylvinylsilane) [Cu(hfac)(tmvs)], which is the most common CVD precursor, cannot be used as an ALD precursor since it does not provide self-limited ALD due to its disproportionation. Cu(thd)2 and Cu(acac)2, which are complexes of Cu(II) β-diketonate, have relatively low vapor pressures and low evaporation rates. Although fluorinated Cu(II) β-diketonate molecules such as Cu(hfac)2 have a higher vapor pressure than non-fluorinated Cu(II) β-diketonate, fluorine atoms in the precursor cause poor adhesion of an ALD copper film to a tantalum-based barrier metal. Recently, a non-fluorinated copper precursor having a high vapor pressure has been synthesized. (Cu(sBu-Me-amd))2 and Cu(ethylketoiminate)2 showed high vapor pressures, and were reduced by H2 so that a pure copper film was deposited on a metal substrate. Further, Cu(dmap)2 and Cu(dmamb)2 have been researched as an ALD precursor using Et2Zn or hydrogen plasma as a reducing agent. However, a thermal ALD of copper using NH3 and/or H2 as a reducing agent has not yet been reported.
Further, a copper film was formed by reducing a copper oxide or copper nitride film. An ALD copper oxide film had a low growth rate of about 0.01 nm/cycle, and was deposited at 100° C. to 160° C. using bis(tri-n-butylphosphine)copper(I)acetylacetonate [(nBu3P)2Cu(acac)] and wet O2 and could be reduced at 115° C. by performing a heat treatment with formic acid vapor. However, an oxidizing agent for ALD of copper oxide also oxidizes a barrier metal on which the copper seed layer is formed. A copper nitride film formed by ALD was deposited using (Cu(sBu-Me-amd))2 and NH3, and reduced to metal copper at 225° C. by reducing annealing with H2(10%)/N2 under 5 Torr. Although a copper film reduced from copper nitride by ALD had superior surface morphology and resistivity compared to those of a copper film formed by ALD, details of a process for the copper nitride by ALD have not been disclosed [Z. Li and R. G. Gordon, “Thin, Continuous, and Conformal Copper Films by Reduction of Atomic Layer Deposited Copper Nitride”, Chemical Vapor Deposition, 2006, volume 12, pages 435-441]. Further, (Cu(sBu-Me-amd))2, which is a solid at room temperature, is more disadvantageous for mass production of semiconductor devices than a copper precursor which is a liquid at room temperature. Since copper atoms in a thin copper film easily aggregate with each other, it is very difficult to form a thin copper film with a high electric conductivity. If copper atoms in a thin copper film aggregate, the copper film cannot be a continuous film but has a surface portion where copper is not present. Such a discontinuous copper film has a high electric resistance and cannot be used as a seed layer for electrodeposition.
The present disclosure relates to a copper metal film, a method for preparing the same, and a method for forming a copper interconnect for a semiconductor device using the copper metal film as a seed layer. Further, the present disclosure provides a precursor for deposition of a copper metal film and a composition containing the same for deposition of a copper metal film. Furthermore, the present disclosure provides a copper interconnect for a semiconductor device formed by the method for forming a copper interconnect for a semiconductor device and a semiconductor device including the same.
However, problems to be solved by the present disclosure are not limited to the above-described problems. Although not described herein, other problems to be solved by the present disclosure can be clearly understood by those skilled in the art from the following descriptions.